Acidification of soil may be needed when soil pH is high or when naturally occurring calcium carbonates are present. For example, when pH is above about 7.5, the solubility of phosphorous and the metal micronutrients such as iron, manganese and zinc are limited. Thus, generating a zone of acidification where the solubility of the fertilizers is enhanced promotes plant growth by increasing nutrient availability.
The acidifying agent that is selected must be safe to work with and preferably should not require special acid-resistant equipment for application. Furthermore, the acidifying agent should not generate significant heat or very acidic conditions on application as very acidic conditions and high salt concentrations can kill microorganisms in the soil or the seed of the crop sown.
U.S. Pat. No. 6,783,567 teaches a sulfur humate granule which is applied to the soil in a band with other fertilizers for soil acidification.